It is known to use various structures together with chemical or other processing tanks or vessels to permit access to the interior of said vessels. Many of these structures involve the use of large bulky attachments that are somewhat difficult to remove when cleaning is required. Several of these prior art closure means contain a plurality of parts that are difficult to clean. In many cases parts become contaminated and can cause serious problems such as when used in the food or pharmaceutical field. Bacteria or other debris can collect in these hard to clean parts and result in contamination of the product being processed.
Also, several of these prior art closures such as those referred to as rolling door closures have no viewing window but rather are constructed of solid panels or parts. While these rolling door closures allow the user to gain entry and provide exit means from a vessel, there is no way to safely view the vessel interior during processing. This could be essential, for example, in chemical processing where change of color or volume or the like is important. Closure means having viewing parts are highly desirable. Those prior art devices that do provide viewing windows usually construct the viewing window from tempered sight glass. It has been found that devices of this nature require frequent replacement of the tempered glass windows because of the frequent failure rate. Tempered glass windows will crack under residual stress and will shatter upon any substantial shock. Also Pyrex type windows do not lend themselves to bolting and unbolting, viewing windows that will not shatter and have a long useful life are also highly desirable. Highly improved viewing windows (Fuseview) with these characteristics are disclosed in U.S. Pat. No. 4,809,862 which issued Mar. 7, 1989.
Also, many viewing windows of prior art devices utilize Pyrex-type materials. In chemical processes viewing of the interior of the vessel is impaired by the product adhering to the window. These windows must be discarded after removal and replaced frequently. The time involved in unbolting the closure, removing the window and rebolting after replacement is significant. In addition, generally, prior art closures use clamping style devices that if opened under pressure could cause a serious failure. This is because when they begin to open the stresses on the component members increases dramatically. This can cause blow-out failure or rapid opening. To prevent this from happening, the prior art devices use an interlocking device to signal electrically or mechanically that pressure is present. The problem is that the interlocking device can be bypassed or fail causing improper operation. A simple, inexpensive structure easily removed and easily cleaned is highly desirable.
To summarize the potential problems in prior art devices are the following points:
(1) relatively expensive and complicated with a plurality of parts;
(2) difficult to reach parts that are easily contaminated;
(3) relatively bulky and extending out to a significant distance from the vessel it is attached to causing potential safety hazzard to users. Also, if space is limited, a small protrusion outwardly from the vessel is important.
(4) difficult to disassemble and clean and reassemble and reattach to the vessel; not sanitary to use;
(5) frequent replacement required of parts especially viewing windows of tempered glass;
(6) interlocking devices that when bypassed can cause faulty operation.